The present invention relates to a fast-wave resonator with stratified grounding planes, particularly to a small size fast-wave resonant antenna with stratified grounding planes which can be installed by surface mounting technology (SMT).
The hidden antenna is receiving more attention with the widespread use of mobile phones. Since the hidden antenna is small in size, it can be arranged into an RF circuit by surface mounting technology, thereby increasing its accuracy and thus improving the quality of the mobile phone.
A patch metal strip is used in a conventional hidden antenna. FIG. 1 shows a patch antenna wherein the medium substrate 11 is located on the grounding plane 12 and the patch 13 is located at the center of the upper surface of the medium substrate 11. Signals can be fed into the antenna from the feed line 14. Such configuration is commonly used in various active antennas.
FIG. 2 shows another kind of patch antenna. The difference between FIG. 2 and FIG. 1 is that the feed line 15 of FIG. 2 is extended along the upper surface of the medium substrate 11 and extended downward along the edge through the via hole of the substrate. Such configuration is used to make a surface mounting antenna.
FIG. 3 shows still another kind of conventional patch antenna which is similar to the patch antenna shown in FIG. 1. The main difference is that the signals are fed into the patch antenna via a probe or a coaxial line. It is obvious that connecting such kind of antenna with other microwave circuits using SMT technology may not be appropriate since a coaxial line needs a microwave connector to connect to an external coaxial cable.
According to a prior research result, the resonant frequency of the metal strip antenna is inversely proportional to .di-elect cons..sub.r +L (.di-elect cons..sub.r being the relative permittivity). Under this restriction, dielectric materials with relative permittivity exceeding 20 are usually necessary for the miniaturized metal strip antennas depicted in FIG. 1 to FIG. 3. Moreover, it is known that limited dimension of the grounding plane greatly influences the performance of the metal strip antenna. Therefore, the dimension of the grounding plane should be greater than that of the patch so that the metal strip can work properly.
Besides, a hidden dielectric antenna used in a general integrated circuit can be designed by utilizing the resonance phenomena of the dielectric materials and coupling energy to a medium resonator via a metal strip or a slot line. However, dielectric materials with high relative permittivity are usually adopted in this kind of dielectric antenna because its size is also inversely proportional to .di-elect cons..sub.r +L .
Observe the simplified model of a monopole antenna depicted in FIG. 4(a), the length of the monopole antenna 42 on the housing of the mobile phone 41 is one-fourth the length of free-space wavelength. FIG. 4(b) shows a simplified model of a helix antenna, which is also used in mobile phones. The total length of this kind of helix antenna 43 is quite near to the free-space wavelength .lambda..sub.0, therefore, it is obvious that both these kinds of antennas are not suitable to be used as hidden antennas in mobile phones. Besides, these two kinds of antennas use their housing as the grounding plane. The dimension of the grounding plane is always large, approximately 2.lambda..sub.0.sup.2 in general design (.lambda..sub.0 being free-space wavelength). The dimension of the grounding plane of the antenna is becoming smaller and smaller for downsizing of the mobile phones, thereby influencing the performance of the antenna.